In the field of Radio Frequency (RF) communications, it is known for a communications device, for example a cellular communications handset to comprise a transceiver circuit, the transceiver circuit comprising a receiver circuit, for example a Very Low Intermediate-Frequency (VLIF) receiver. Typically, such receiver circuits are arranged to receive an RF signal and process, separately, an in-phase (I) component and a quadrature (Q) component of the RF signal. The in-phase component is mixed with a real component of an oscillating signal (Cos(ωLot)), the resultant signal being subjected to an anti-aliasing filter before being provided to a real Analogue-to-Digital Converter (ADC) followed by digital filtering. Similarly, the quadrature component of the RF signal is mixed with a complex component of the oscillating signal (−Sin(ωLot)), the resultant signal being subjected to another anti-alias filter before being provided to another real ADC and then subjected to digital filtering. The result of mixing the in-phase and quadrature components of the RF signal with the respective real and imaginary components of the oscillating signal is effectively to scale the RF signal by an exponential complex function resulting in the frequency of the RF signal being “down converted” to a so-called intermediate frequency.
In order to attenuate quantization noise, the design of the ADCs is such that a Noise Transfer Function (NTF) associated with the ADCs has at least one “zero” (point of high attenuation) at predetermined frequencies from 0 Hz (DC) to 200 kHz, for example at 180 kHz. However, due to a symmetric frequency response about DC of two real ADCs, zeros at respective corresponding negative frequencies also exists. The provision of zeros at both negative and positive frequencies through use of the real ADCs results in unnecessary power consumption, since only positive frequency RF signals need to be processed in the VLIF receiver. In order to avoid the provision of zeros in a negative frequency range, and hence reduce power consumption, a so-called complex ADC is employed, the NTF of the complex ADC only having zeros in the positive frequency range. Complex ADCs typically comprise a first real integrator, coupled to a second real integrator so as to provide a complex pole. However, where other ADC functionality is required in a transceiver integrated circuit, separate ADCs comprising integrators need to be separately provided. The provision of separate ADCs with their separate integrators has a die area cost associated therewith.